Guide for use React Native in existing iOS app

See #483

docs/EmbededApp.md

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+---
+id: embeded-app
+title: Use React Native in Existing iOS App
+layout: docs
+category: Guides
+permalink: docs/embeded-app.html
+next: activityindicatorios
+---
+
+## Install React Native Using Cocoapods
+
+[Cocoapods](http://cocoapods.org/) is a package management tool for iOS/Mac development. We need to use it to download React Native. If you haven't install Cocoapods yet, checkout [this tutorial](http://guides.cocoapods.org/using/getting-started.html).
+
+When you are ready to work with Cocoapods, add the following line to `Podfile`. If you don't have one, then create it under the root directory of your project.
+
+	pod 'React'
+	pod 'React/RCTText'  
+	# Add any subspecs you want to use in your project
+
+Remember to install all subspecs you need. The `<Text>` element cannot be used without `pod 'React/RCTText'`.
+	
+Then install pods via shell
+
+	$ pod install --verbose
+	
+The installation process also requires [Node.js](http://nodejs.org).
+
+## Create Your React Native App
+
+First, enter React Native's pod root directory and create **index.ios.js** inside a directory `ReactComponent`.
+
+	$ cd Pods/React
+	$ mkdir ReactComponent
+	$ touch index.ios.js
+	
+Copy & paste following starter code for **index.ios.js**.
+
+	var React = require('react-native');
+
+	var {
+	  Text
+	} = React;
+	
+	class SimpleApp extends React.Component {
+	  render() {
+	    return <Text>This is a simple application.</Text>
+	  }
+	}
+	
+	AppRegistry.registerComponent('SimpleApp', () => SimpleApp);
+	
+`SimpleApp` will be your **module name**, which will be used later on.
+
+## Add Container View To Your App
+
+You should now add container view for React Native component. It can be any **UIView** in your app.
+
+![Container view example](http://7qn8cx.com1.z0.glb.clouddn.com/c37deb761ce048225989ece06cf3d185061c511d-74d3e6b285e1b5cd93153c39fca63c63838b8dbf.png?imageView2/2/h/400/w/400/q/85)
+
+However, let's subclass **UIView** for the sake of clean code. Let's name it **ReactView**. Open up **Yourproject.xcworkspace** and create a new class **ReactView** (You can name it whatever you like :)).  
+
+	// ReactView.h
+	
+	#import <UIKit/UIKit.h>
+	@interface ReactView : UIView
+	@end
+
+
+Don't forget to add an outlet for it.
+	
+	// ViewController.m
+
+	@interface ViewController ()
+	@property (weak, nonatomic) IBOutlet ReactView *reactView;
+	@end
+	
+Here I disabled **AutoLayout** for simplicity. In real production world, you should turn on AutoLayout and setup constraints by yourself.
+
+## Add RCTRootView To Container View
+
+Ready for the most interesting part? Now we shall create the **RCTRootView**, where your React Native app lives in. 
+
+In **ReactView.m**, we need to first initiate **RCTRootView** with the URI of your **index.ios.bundle**. **index.ios.bundle** will be created by packager and served by React Native server, which will be discussed later on.
+
+    NSString *urlString = @"http://localhost:8081/index.ios.bundle";
+    NSURL *jsCodeLocation = [NSURL URLWithString:urlString];
+    RCTRootView *rootView = [[RCTRootView alloc] initWithBundleURL:jsCodeLocation
+                                                        moduleName: @"SimpleApp"
+                                                     launchOptions:nil];
+Then add it as a subview of the **ReactView**.
+
+    [self addSubview:rootView];
+    rootView.frame = self.bounds;
+    
+## Start Development Server
+
+In root directory, we need to start React Native development server. 
+
+	$ ./Pods/React/packager/packager.sh --root ./ReactComponents
+	
+`--root` indicates the root of your React Native apps. Here we just have one **index.ios.js**. React Native development server will use packager to create a **index.ios.bundle**. Which can be access via `http://localhost:8081/index.ios.bundle`.
+
+## Compile And Run
+
+Now compile and run your app. You shall now see your React Native app running inside of the **ReactView**.
+
+![Example](http://7qn8cx.com1.z0.glb.clouddn.com/0c4e7b977f1db688b60f1579a581f30dd1abc85f-86bebe4092e82c395e322fefcc8f7727b0820ac7.png?imageView2/2/h/400/w/400/q/85)
+
+## Conclusion
+
+So under the hood, when **RCTRootView** is initialized, it will try to download, parse and run the bundle file from React Native development server. All you need to do is to implement your own container view, add **RCTRootView** as its subclass. And then serve the bundle using React Native development server. Then, bravo!
+
+You can checkout full source code of sample application [here](https://github.com/tjwudi/EmbededReactNativeExample).